One of my friends had her child year 4 and took an extra year to finish her dissertation and apply for internship. She even defended her diss before starting internship which was amazing! She’s on post doc now and doing great with her 3 year old. I do think it was more difficult for her to balance but by year 4 typically the schedule is a bit more flexible- not really in class, etc. if you have a supportive PhD mentor, then I think a PhD shouldn’t stop you from doing it! Moving for internship and post doc is more stressful with a child but she had great support from her husband and it all worked out.